Comparison of genomic sequences of several organisms with sequence databases reveals that a large fraction of proteins coded by the genes have not known functions and/or structures. Structures of these proteins may provide additional key information for the discovery of the molecular functions of these proteins and the relationship with their three-dimensional folds. Three-dimensional structures of the majority of the proteins from a minimal genome (Mycoplasma genitalium/pneumoniae) or their homologues, for which no functions and/or structures are known, will be determined by X-ray crystallographic methods.